Make offsets to inner allocated objects aligned in allocation folding.

Folded allocations marked for double alignment is not aligned if old dominator
size is used for offset to inner object.

TEST=mjsunit/big-array-literal on MIPS
BUG=
R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/103963005

Patch from Dusan Milosavljevic <Dusan.Milosavljevic@rt-rk.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18332 ce2b1a6d-e550-0410-aec6-3dcde31c8c00